This invention relates to wireless communication systems and, more particularly, to methods for assignment of system transmission parameters for high speed transmission in such communication systems.
Wireless communication systems have been developed to allow transmission of information signals between an originating location and a destination location. Both analog (first generation) and digital (second generation) systems have been developed to transmit information signals over communication channels linking the source and destination locations. Digital methods tend to afford several advantages over analog systems. For example, improved immunity to channel noise and interference, increased capacity, and encryption for secure communications are advantages of digital systems over analog systems.
While first generation systems were primarily directed to voice communication, second generation systems support both voice and data applications. Numerous techniques are known in second-generation systems for handling data transmissions which have different transmission requirements. In particular, data transmissions, typically, are of relatively short duration whereas voice transmission is of a longer duration and requires continuous access to the communication channel. Several modulation/coding arrangements have been developed, such as frequency division multiple access (FDMA), time division multiple access (TDMA), and code division multiple access (CDMA), to increase the number of users that can access a wireless network. CDMA systems are more immune to multiple path distortion and co-channel interference than FDMA and TDMA systems and reduce the burden of frequency/channel planning that is common with FDMA and TDMA systems.
In a CDMA system, a unique binary code sequence is assigned to each active user within a cell to uniquely identify the user and spread the user""s signal over a larger bandwidth. Multiplied by the assigned code, the user""s signal is spread over the entire channel bandwidth, which is wider than the user""s signal bandwidth. The ratio of the system channel bandwidth to the user""s bandwidth is the xe2x80x9cspreading gainxe2x80x9d of the system. The capacity of the CDMA system is proportional to the xe2x80x9cspreading gainxe2x80x9d for a given signal-to-interference (S/I) level. After reception of the transmitted signal, the signal of each user is separated, or de-spread, from the signals of other users by using a correlator keyed to the code sequence of the desired signal.
First-generation analog and second-generation digital systems were designed to support voice communication with limited data communication capabilities. Third-generation wireless systems, using wide-band multiple access technologies such as CDMA, are expected to effectively handle a large variety of services, such as voice, video, data and imaging. Among the features which will be supported by third-generation systems is the transmission of high-speed data between a mobile terminal and a land-line network. As is known, high-speed data communications is often characterized by a short transmission xe2x80x9cburstxe2x80x9d at a high data transmission rate, followed by some longer period of little or no transmission activity from the data source. To accommodate the bursty nature of such high-speed data services in third-generation systems, it is necessary for the communications system to assign a large bandwidth segment (corresponding to the high data rate) from time to time for the duration of the data burst. With the ability of the third generation systems to handle such bursty high-speed data transmission, throughput and delay for users can be advantageously improved. However, because of the large amount of instantaneous bandwidth required for transmission of a burst of high-speed data, the management of such bursts, and particularly the allocation of power and system resources thereto, must be handled with care to avoid unwarranted interference with other services using the same basic frequency allocation.
In establishing a high speed burst communication link, a land-line network base station and a mobile terminal (or station) agree upon a service configuration that is to be used by the base station and the mobile station. Transmission data rate and nominal initial output power are service configuration parameters that must be assigned before the burst transmission can begin. During the establishment of the communication link, a prearranged protocol of command messages and responses are exchanged between the base station and the mobile station. Among these protocol messages is a request, made by the base station, for a measure of the signal strength received at the mobile station. The base station requests the signal strength measurement be performed by transmitting a Pilot Measurement Request Order (PMRO) message. The mobile station, in response, measures the received signal strength, and returns this measurement to the base station through the Pilot Signal Measurement Message (PSMM). The base station then assigns the burst transmission parameters with a goal of providing an acceptable quality of service using a minimum of system resources.
To maintain acceptable signal reception and quality, with a minimum of system resources, it would be advantageous to adjust the base station initial output power level, transmission data rate and bandwidth in response to the dynamics of the wireless environment. However, to continuously adjust the transmission parameters requires the base station to repeatedly request that the mobile station report the received signal strength each time the mobile station makes a burst request. Each such request introduces delay in the transmission of the burst and contributes to an inefficient utilization of the channel resources.
It is an object of the invention to improve the efficiency of the communication link utilization in a wireless communication network by making system parameters of remote sites available to local controllers. It is a further object of the invention to provide a method of reporting system parameters from remote sites to local controllers in an efficient manner. It is a still further object of the invention to reduce the time required to assign burst transmission parameters by providing system parameter data to a local controller in a efficient manner. It is a further object of the invention to provide a method of obtaining system data that may be used to dynamically assign burst transmission parameters during a burst transmission.
According to the method of the invention, remote sites autonomously report system data to a local controller and the local controller uses this information to allocate transmission parameters and improve system performance. More specifically, in a wireless communication network, after a local controller, such as a base station, and a remote site, such as a mobile station, have established a communication link for burst transmissions, the remote site mobile station autonomously reports system parameter information to the local controller base station such that the local controller may adjust the burst transmission parameters based on the reported signal parameter values.
Further, the base station collects the reported system parameters and in combination with base-station-specific system information, such as cumulative power history and Signal to Interference Ratio (SIR), reports this information, via its associated link, to a mobile switching center, which is a local controller of a network of base stations.
In a further embodiment of the invention, both the base station and the mobile station employ time-out arrangements, such that if data is not received within known time periods from the last data message received, the data session between the mobile station and the base station is deemed ended (cleared) and the mobile station and base station proceed to end their communication link processing.
In accordance with the method of the invention, and with specific applicability to the communication link between a mobile station and a base station, the autonomous reporting of such data as the measured signal strength provides the base station with information to update and optimize burst transmission parameters, without delaying the transmission and without incurring channel overhead that otherwise would be necessary to obtain this information. Thus, the invention provides an improvement in system operation without incurring the expense of delayed transmissions or inefficient channel utilization.